36. Red-Black Trees

36.1. Introduction

The Red-Black Tree API is an interface to the SuperCore (score) rbtree implementation. Within RTEMS, red-black trees are used when a binary search tree is needed, including dynamic priority thread queues and non-contiguous heap memory. The Red-Black Tree API provided by RTEMS is:

  • rtems_rtems_rbtree_node - Red-Black Tree node embedded in another struct

  • rtems_rtems_rbtree_control - Red-Black Tree control node for an entire tree

  • rtems_rtems_rbtree_initialize - initialize the red-black tree with nodes

  • rtems_rtems_rbtree_initialize_empty - initialize the red-black tree as empty

  • rtems_rtems_rbtree_set_off_tree - Clear a node’s links

  • rtems_rtems_rbtree_root - Return the red-black tree’s root node

  • rtems_rtems_rbtree_min - Return the red-black tree’s minimum node

  • rtems_rtems_rbtree_max - Return the red-black tree’s maximum node

  • rtems_rtems_rbtree_left - Return a node’s left child node

  • rtems_rtems_rbtree_right - Return a node’s right child node

  • rtems_rtems_rbtree_parent - Return a node’s parent node

  • rtems_rtems_rbtree_are_nodes_equal - Are the node’s equal ?

  • rtems_rtems_rbtree_is_empty - Is the red-black tree empty ?

  • rtems_rtems_rbtree_is_min - Is the Node the minimum in the red-black tree ?

  • rtems_rtems_rbtree_is_max - Is the Node the maximum in the red-black tree ?

  • rtems_rtems_rbtree_is_root - Is the Node the root of the red-black tree ?

  • rtems_rtems_rbtree_find - Find the node with a matching key in the red-black tree

  • rtems_rtems_rbtree_predecessor - Return the in-order predecessor of a node.

  • rtems_rtems_rbtree_successor - Return the in-order successor of a node.

  • rtems_rtems_rbtree_extract - Remove the node from the red-black tree

  • rtems_rtems_rbtree_get_min - Remove the minimum node from the red-black tree

  • rtems_rtems_rbtree_get_max - Remove the maximum node from the red-black tree

  • rtems_rtems_rbtree_peek_min - Returns the minimum node from the red-black tree

  • rtems_rtems_rbtree_peek_max - Returns the maximum node from the red-black tree

  • rtems_rtems_rbtree_insert - Add the node to the red-black tree

36.2. Background

The Red-Black Trees API is a thin layer above the SuperCore Red-Black Trees implementation. A Red-Black Tree is defined by a control node with pointers to the root, minimum, and maximum nodes in the tree. Each node in the tree consists of a parent pointer, two children pointers, and a color attribute. A tree is parameterized as either unique, meaning identical keys are rejected, or not, in which case duplicate keys are allowed.

Users must provide a comparison functor that gets passed to functions that need to compare nodes. In addition, no internal synchronization is offered within the red-black tree implementation, thus users must ensure at most one thread accesses a red-black tree instance at a time.

36.2.1. Nodes

A red-black tree is made up from nodes that orginate from a red-black tree control object. A node is of type rtems_rtems_rbtree_node. The node is designed to be part of a user data structure. To obtain the encapsulating structure users can use the RTEMS_CONTAINER_OF macro. The node can be placed anywhere within the user’s structure and the macro will calculate the structure’s address from the node’s address.

36.2.2. Controls

A red-black tree is rooted with a control object. Red-Black Tree control provide the user with access to the nodes on the red-black tree. The implementation does not require special checks for manipulating the root of the red-black tree. To accomplish this the rtems_rtems_rbtree_control structure is treated as a rtems_rtems_rbtree_node structure with a NULL parent and left child pointing to the root.

36.3. Operations

Examples for using the red-black trees can be found in the testsuites/sptests/sprbtree01/init.c file.

36.4. Directives

36.4.1. Documentation for the Red-Black Tree Directives

Source documentation for the Red-Black Tree API can be found in the generated Doxygen output for cpukit/sapi.